Analysis of fractional order systems using newton iteration-based approximation technique

Fractional differential equations play a major role in expressing mathematically the real-world problems as they help attain good fit to the experimental data. It is also known that fractional order controllers are more flexible than integer order controllers. But when it comes to the numerical approximation of fractional order functions inaccuracies arise if the conversion technique is not chosen properly. So, when a fractional order plant model is approximated to an integer order system, it is required that the approximated model be accurate, as the overall system performance is based on the estimated integer order model. Nitisha-Pragya-Carlson (NPC) is a recent approximation technique proposed in 2018 to derive the rational approximation of fractional order differ-integrators. In this paper, three fractional order plant models having fractional powers 3.1, 1.25 and 1.3 is analyzed in frequency domain in terms of magnitude and phase response. The performance of approximated third and second order NPC based integer model is studied and compared with the integer models developed using other existing technique. The approximation error is calculated by comparing the frequency response of the developed models with the ideal response. It has been found that in all the three examples NPC based models are very much close to the ideal values. Hence proving the efficacy of NPC technique in approximation of fractional order systems

Study of pump control in residential grid-tied solar domestic hot water photovoltaic-thermal (PV-T) systems

A study of pump control focusing on active residential grid-connected solar domestic hot water (SDHW) photovoltaic-thermal (PV-T) systems was conducted. The main goal was to determine how the two main pump controls for this segment compare, namely the differential temperature static two-level hysteretic control (DTSTLHC) and the differential temperature static saturated hysteretic-proportional control (DTSSHPC), given the dual outputs of PV-T technology: heat and electricity. In order to do so, a dynamic PV-T collector model was developed for use in transient simulations and incorporated into a SDHW PV-T system model. A substantial number of annual simulations for each of the various locations selected were conducted to encompass the best performances using each control, with emphasis on multiple combinations of controller setpoints and mass flow rates. The results show PV-T systems using DTSSHPC and optimised for maximum auxiliary energy savings consistently outperforming those using DTSTLHC and optimised using the same criterion, though the opposite was true when seeking to optimise the electrical efficiency, with those using DTSTLHC performing best. However, the advantages at best correspond to single-digit percentages of the annual thermal energy demand, and less than 0.1% of the annual electrical efficiency. Similarly low performance advantages were reached from the standpoint of primary energy efficiency and load provision cost-effectiveness by using DTSSHPC, though not consistently due to the inability to reconcile electrical, thermal and parasitic performance advantages over DTSTLHC. Moreover, the advantages presented by DTSSHPC are low enough to be offset by one additional maintenance operation, which systems using this control are likelier to require first due to its complexity and higher switching frequencies. Finally, a study on setpoint selection for differential temperature controllers, namely DTSSHPC and DTSTLHC, for use in PV-T systems was also conducted using steady-state methods, which revealed marginal differences between setpoint selection for hybrid and non-hybrid systems

Symmetry in Renewable Energy and Power Systems

This book includes original research papers related to renewable energy and power systems in which theoretical or practical issues of symmetry are considered. The book includes contributions on voltage stability analysis in DC networks, optimal dispatch of islanded microgrid systems, reactive power compensation, direct power compensation, optimal location and sizing of photovoltaic sources in DC networks, layout of parabolic trough solar collectors, topologic analysis of high-voltage transmission grids, geometric algebra and power systems, filter design for harmonic current compensation. The contributions included in this book describe the state of the art in this field and shed light on the possibilities that the study of symmetry has in power grids and renewable energy systems

ThermoSolar and photovoltaic hybridization for small scale distributed generation : applications for powering rural health

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 213-223).The problem of provisioning a remote health clinic or school with electricity, heating and cooling (trigeneration) is considered from an engineering design and optimization standpoint. A baseline technical-economic review of existing options is performed, and a novel alternative is proposed: micro-Concentrating Solar Power (CSP), featuring an Organic Rankine Cycle (ORC) using repurposed HVAC scroll compressors as expanders. The design of the [mu]-CSP technology is informed by a semi-empirical steady state multi-physics sizing and performance model (SORCE) which predicts system output, efficiency, and specific costs as a function of geoposition. Empirical validation of key mechanical and electrical components is performed to parameterize the model. On a levelized cost basis, ,-CSP is shown to outperform standard equipment for trigeneration applications at remote sites. Scroll expander development is identified as an opportunity for enhanced performance, and a computationally efficient method for selecting optimal thermo-mechanical geometries for a scroll expander is described. Tradeoffs between concentration ratio, power block size and thermal storage are examined, and the key role of thermal capacity in the system is highlighted. A semi-dynamic version of SORCE is developed to support optimization amongst system components in a simulated operating environment including insolation and thermal transients; this offers preliminary insights into control decisions that influence cost and performance, such as timing and power management of ORC operation. Finally, the concept of synergies between concentrating solar photovoltaic (CPV) and CSP architecture is explored. A semi-empirical diode model is developed using experimental data from commercially available a-SI and c-Si solar cells and incorporated into PV-SORCE (where the [mu]-CSP thermal absorber is replaced with a PV heat collection element). Optimization of design parameters influencing figures of merit (system efficiency and specific costs) indicates that an optimal configuration is highly sensitive to the PV properties; as such, further optimization of the hybrid system parameters is recommended. This research also involved lab and field (Lesotho, southern Africa) prototyping of small solar ORC units. Relevant design parameters and further development of the [mu]-CSP concept is discussed in the context of field experiences.by Matthew S. Orosz.Ph.D

Advanced surface and volumetric receivers to convert concentrated solar radiation

This thesis is the results of the work conducted during the three years of Ph.D. at the Department of Industrial Engineering of the University of Padova. The conversion of solar energy into heat in the medium-temperature range (between 80 °C and 250 °C) has recently encountered a renewed interest in heating and cooling applications of industrial, commercial, residential and service sectors. Concentrating solar thermal collectors at medium temperature are suitable for many commercial and industrial applications, such as industrial process heat, solar cooling and desalination of the seawater. It is expected that in the future, a significant technological development can be achieved for these collectors, provided that the conversion of solar energy becomes more efficient and cost-effective. The proper design of the receiver, which is considered the heart of any concentrating collector, is essential to the future improvement in the conversion efficiency of this technology. In this context, the present thesis investigates the application of two innovative concepts of receivers in a prototype of an asymmetrical parabolic trough concentrator installed in the Solar Energy Conversion Lab of the Industrial Engineering Department, at the University of Padova. In Chapter 1, a study on different estimation procedures for the assessment of the direct normal irradiance, which is the solar resource utilized by solar concentrators, is presented. The study includes an indirect evaluation from measurements of global and diffuse horizontal irradiances and the use of semi-physical/empirical models. A detailed analysis of the instrumentation and of the measuring technique as well as the expression of the experimental uncertainty is provided. In Chapter 2, the optical performance of the asymmetrical parabolic trough is experimentally characterized. As a result, a statistical ray-tracing model of the concentrator for optical performance analysis in different working conditions is validated and used to optimize the design of the proposed receivers. In Chapter 3, an innovative flat aluminium absorber manufactured with the bar-and-plate technology, including an internal turbulator, is tested in the asymmetrical parabolic trough collector under single-phase and two-phase flow regimes. A numerical model to predict its performance has been developed and validated against the experimental data. In Chapter 4, this model is used to evaluate the performance of a small solar-powered ORC system by coupling the aforementioned concentrating solar system with direct vaporization of a low-GWP halogenated fluid or by using an intermediate solar circuit to heat pressurized water and evaporate the same organic working fluid in a separate heat exchanger. Finally, in Chapter 5 a new direct absorption receiver is proposed to investigate the capability of a suspension of single-wall carbon nanohorns in distilled water to absorb concentrated sunlight. The volumetric receiver has been designed through the development of a three-dimensional computational fluid dynamics model for its installation in the focus region of the asymmetrical parabolic trough. The capability of the nanofluid in collecting solar radiation when exposed to concentrated and non-concentrated solar flux are experimentally investigated thanks to the cooperation with National Council of the Research (CNR), that provided the aqueous solution. The nanofluid was tested in several conditions, with and without circulation, to investigate its stability with time